A technique to reduce the frame frequency is known as a method for reducing the consumed power of liquid crystal displays. For example, the following technique is suggested. A rest period in which all the scan signal lines are in a non-scan state is set between scan periods in which the screen is scanned. In the rest period, the operation of a driving circuit for driving a display portion is stopped.
On the other hand, when the frame frequency is reduced, the voltage retained by each pixel tends to change as time passes. Thus, in the displayed image, the difference in luminance may be easily recognized as a flicker because of the difference in potential between frames. In this manner, the display quality may be degraded.